In a variator serving as a principal part of a full-toroidal continuously variable transmission, an input disk and an output disk each having a concaved track surface are arranged such that the track surfaces are opposed to each other, and a plurality of rollers are arranged between both the disks (see Japanese Unexamined Patent Publication Nos. 2002-174315, 2004-278740, and 2001-74114, for example).
A terminal load due to the hydraulic pressure of traction oil is applied in an axial direction of each of the disks. This causes the rollers to be press-contacted to the track surface of each of the disks through an oil film. The input disk is attached to an input shaft whose rotation is driven by a driving source of a vehicle, for example, an engine. The rotation of the input shaft transmits torque to the output disk from the input disk through the rollers.
The axis of rotation of the rollers is inclined depending on necessary torque so that transmission is performed in a stepless manner (see International Patent Application Publication No. WO 91/14116, for example). The axis of rotation of the rollers is supported by a carriage serving as a supporting member. There is provided a hydraulic cylinder for applying a driving force in a traveling direction of the carriage, and thus adjusting a biasing force of the rollers against both the disks.
As disclosed in Japanese Unexamined Patent Publication Nos. 2002-174315 and JP 2004-278740, the hydraulic cylinder has a pair of oil chamber. Oil from a hydraulic pump is introduced into one of the oil chambers, and oil in the other oil chamber is discharged into a tank. The driving force in the traveling direction is produced on the basis of a differential pressure between the oil chambers.
In the full-toroidal continuously variable transmission, when the torque is transmitted from the input disk to the output disk, a traction force is produced between the rollers and each of the disks. The end load and the driving force of the carriage are set such that the traction force and the driving force of the carriage are balanced under a predetermined traction coefficient.
In recent years, there has been a request to miniaturize a full-toroidal continuous variable transmission. For this purpose, it is preferable that a hydraulic pump for biasing rollers is miniaturized. When a small-sized hydraulic pump is used, however, a hydraulic cylinder cannot quickly feed hydraulic oil corresponding to a rapid transmission. As a result, responsiveness at the time of transmission is restricted.